Heat 2 tbsp oil in large skillet over medium heat. Add the onion and saute for 3 to 5 minutes until translucent, then add the garlic, thyme, tarragon, salt and pepper, and cook for another minute. Next, add the mushrooms and cook for 7 to 10 minutes until they are very soft, lowering the heat if necessary to prevent them from burning.

While the mushrooms are cooking, place the walnuts in a food processor or blender and pulse until fine.

Add the cooked mushroom mixture to the walnuts in the food processor, along with the balsamic vinegar, beans and remaining tbsp olive oil. Process until smooth, adding the veggie broth 1 tbsp at a time as needed. Continue to puree until the pate resembles a smooth, thick and spreadable paste. Scrape mixture into an airtight container and chill for at least an hour before serving, to allow the flavors to meld.